L deficit is exacerbated when local visual cues have to be integrated across multiple (>2) dimensions. Impairment was most marked on the random-dot global motion task and the temporally-defined global form task, as indicated by the effect sizes in Tables 4 and 6. Both of these tasks required integration of local visual cues across two dimensions of space as well as over time. If this explanation is valid then generally poor readers and individuals with dyslexia should also exhibit deficits on a range of other visual tasks. For example, accurately encoding the global motion of an object defined purely by stereoscopic (cyclopean) depth cues requires combination of visual information across four dimensions (x, y, z, t) and may be extremely challenging for the least skilled readers. Future research aimed at testing this and PeficitinibMedChemExpress ASP015K related predictions should help to refine the contribution of task complexity to the profile of visual impairment in dyslexia. Our results also cast further doubt on the noise-exclusion hypothesis of dyslexia, since a difficulty in segregating signal from noise elements would be expected to impair performance on all four visual tasks but this was not the case. This suggests that noise exclusion (Sperling et al., 2005, 2006) in itself is not the proximal cause of the perceptual deficit shown in generally poor readers and individuals with dyslexia. However, it may be possible to reconcile this theory with the present results if we assume that theseR. Johnston et al. / Brain and Cognition 108 (2016) 20?individuals exhibit some difficulties with external-noise exclusion but only when high levels of noise are present in tasks that require integration of visual information over time. A recent study has shown that readers with dyslexia have elevated levels of choline and glutamate in visual cortex, leading to hyperexcitability and Entinostat custom synthesis increased susceptibility to noise (Che, Girgenti, LoTurco, 2014; Pugh et al., 2014). Consequently, it would be interesting to investigate if coherence thresholds on the spatially 1-D global motion task, the random-dot global motion task, and the temporallydefined global form fpsyg.2017.00209 task are associated with neurometabolic concentration in visual cortex. It is interesting to note that after controlling for the effects of Gender and Non-Verbal IQ, Reading skill explained more of the variance (10 ) in performance on the temporally-defined global form task than any of the other visual tasks. Unlike the other three visual tasks the temporally-defined form task fpsyg.2017.00209 requires some degree of segmentation, as well as integration, of local cues. That is, to identify the global orientation of the perceptual boundary visual information provided by temporally asynchronous jitter cues must be integrated within each half of the display but also segmented from those in the opposing half of the image. That reading ability was the strongest predictor of performance on this particular task is consistent with previous studies that have investigated motion segmentation in poor readers (Hill Raymond, 2002). Our results also showed that Non-Verbal IQ was negatively associated with coherence thresholds on the spatially 1-D global motion task and the random-dot global motion task in both the whole-sample and between-group analyses. Previous research has reported a link between intelligence and motion processing (Melnick et al., 2013). The differential performance of individuals with relatively low and high IQs might reflect differen.L deficit is exacerbated when local visual cues have to be integrated across multiple (>2) dimensions. Impairment was most marked on the random-dot global motion task and the temporally-defined global form task, as indicated by the effect sizes in Tables 4 and 6. Both of these tasks required integration of local visual cues across two dimensions of space as well as over time. If this explanation is valid then generally poor readers and individuals with dyslexia should also exhibit deficits on a range of other visual tasks. For example, accurately encoding the global motion of an object defined purely by stereoscopic (cyclopean) depth cues requires combination of visual information across four dimensions (x, y, z, t) and may be extremely challenging for the least skilled readers. Future research aimed at testing this and related predictions should help to refine the contribution of task complexity to the profile of visual impairment in dyslexia. Our results also cast further doubt on the noise-exclusion hypothesis of dyslexia, since a difficulty in segregating signal from noise elements would be expected to impair performance on all four visual tasks but this was not the case. This suggests that noise exclusion (Sperling et al., 2005, 2006) in itself is not the proximal cause of the perceptual deficit shown in generally poor readers and individuals with dyslexia. However, it may be possible to reconcile this theory with the present results if we assume that theseR. Johnston et al. / Brain and Cognition 108 (2016) 20?individuals exhibit some difficulties with external-noise exclusion but only when high levels of noise are present in tasks that require integration of visual information over time. A recent study has shown that readers with dyslexia have elevated levels of choline and glutamate in visual cortex, leading to hyperexcitability and increased susceptibility to noise (Che, Girgenti, LoTurco, 2014; Pugh et al., 2014). Consequently, it would be interesting to investigate if coherence thresholds on the spatially 1-D global motion task, the random-dot global motion task, and the temporallydefined global form fpsyg.2017.00209 task are associated with neurometabolic concentration in visual cortex. It is interesting to note that after controlling for the effects of Gender and Non-Verbal IQ, Reading skill explained more of the variance (10 ) in performance on the temporally-defined global form task than any of the other visual tasks. Unlike the other three visual tasks the temporally-defined form task fpsyg.2017.00209 requires some degree of segmentation, as well as integration, of local cues. That is, to identify the global orientation of the perceptual boundary visual information provided by temporally asynchronous jitter cues must be integrated within each half of the display but also segmented from those in the opposing half of the image. That reading ability was the strongest predictor of performance on this particular task is consistent with previous studies that have investigated motion segmentation in poor readers (Hill Raymond, 2002). Our results also showed that Non-Verbal IQ was negatively associated with coherence thresholds on the spatially 1-D global motion task and the random-dot global motion task in both the whole-sample and between-group analyses. Previous research has reported a link between intelligence and motion processing (Melnick et al., 2013). The differential performance of individuals with relatively low and high IQs might reflect differen.
